Generally mixed in a liquid such as bunker C, which is a main fuel for a marine diesel engine, are alumina, silica, carbon or other hard particles as residue in fluid catalytic cracking (FCC) for petroleum refinery.
Excessive inflow of such hard particles into the engine with a piston ring, a cylinder liner and the like may cause adverse effects such as degraded sliding, seizing-up and mechanical wear. Thus, every time fuel is replenished, a ship management company samples and chemically analyzes the fuel to quantitatively grasp the hard particles in the fuel. When fuel with hard particles of not less than a stipulated concentration is replenished to a ship, the fact is notified of to the ship's crew to call their attention.
Conventionally, when hard particles in fuel are to be detected, sampled fuel is filtered through a filter or the like and a residue is microscopically observed or quantitatively analyzed to detect hard particles.
State-of-the-art technology with respect to a hard particle concentration detecting method is shown, for example, in Patent Literature 1.